1. Field of the Invention
The invention relates to an inkjet printhead assembly.
2. Description of the Related Art
There is known an inkjet printhead assembly including a head unit and a planar piezoelectric actuator attached to the head unit. The head unit has an ink supply port connected via an ink supply channel to an ink supply source storing ink and receives the ink from the ink supply source. The head unit further has a plurality of pressure chambers formed in the head unit, and a large number of nozzles respectively communicated with the pressure chambers. When the ink in each pressure chamber is selectively pressurized, a droplet of the ink is ejected through the corresponding one of the nozzles.
To the ink supply port of the head unit is connected a channel structure of resin through which the ink supply channel extends so that the ink is supplied into the head unit from the ink supply source. A filter member for filtering out foreign materials such as dirt is attached to cover the ink supply port, since introduction of foreign materials into the ink supply port leads to clogging of the nozzles or other portions which causes failure in ejection of ink droplets.
Thus, at a portion where the ink supply port is disposed, the filter member and the resin channel structure are attached.
The filter member and the channel structure are typically connected by bonding or welding. The ink supply port is formed in a base plate of metal such as nickel alloy, and the filter member is typically of metal such as nickel alloy. To assemble the three members, namely, the filter member, the channel structure, and the base plate, the metallic filter member is bonded to the metal base plate, and the resin channel structure is bonded to the metallic filter member. The resin channel structure may be fixed to the filter member or the base plate by ultrasonic welding, not by bonding with adhesive.
Such a filter member has a large number of minute filter holes having a diameter smaller than that of the nozzles. Since the filter member functions as intended only when the diameter of the filter holes is sufficiently small, the diameter of the filter holes is limited, and a filtering area across which the filter holes are formed in the filter member is made accordingly large in order to compensate for the increase in the resistance of the filter holes to the ink flow due to the limited diameter of the filter holes. Thus, in the filter member, a great number of very small holes are formed over an area corresponding to each ink supply port.
As the filter member, there are known a mesh filter using cloth of fiber or thin wire where the small clearances between the fibers or wires serve as filter holes, as well as a filter of thin metal sheet having filter holes each in a circular shape, for instance. Such a metal filter is formed by etching or electroforming.
Etching and electroforming are preferable as a method for forming the metal filter, since these enable to reduce the thickness of the metal filter. Between the two methods, however, electroforming is more preferable, since electroforming enables to form the filter holes with higher precision in shape, compared with etching.
Meanwhile, there is already disclosed, for instance in Japanese Patent Application Laid-Open No. 2001-239677 (see pages 1-6 and FIG. 2), an inkjet printhead assembly including a filtering arrangement such that a filter member is placed in a recess and a clearance between the filter member and each of a channel structure and an inner wall of the recess is filled with an adhesive material.
In manufacture of such an inkjet printhead assembly, where the filter member and the channel structure are bonded to each other with an adhesive, the working process is relatively simple and involved operations are relatively easy. However, because of a change in temperature around the filtering arrangement or for other reasons, the bonding strength between the filter member and the channel structure may later deteriorate, and the filter member and the channel structure may be separated from each other. In addition, since the channel structure is an annular member having a relatively small thickness, the width of the annular area at which the channel structure is bonded to the filter member is relatively small, leading to an insufficient bonding strength therebetween. Thus, it is required to enhance the bonding strength.
On the other hand, the method in which the filter member is placed in the recess and the clearance is filled with the adhesive material requires, in manufacture of the inkjet printer, a step for forming the recess in a depth corresponding to the filter member as well as a step for filling the recess with the adhesive material. Hence, this method fails to shorten or simplify the manufacturing process.